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Metabolism and digestibility trials were performed on broiler chickens to determine 1) nitrogen-corrected apparent metabolizable energy (AMEn) using total excreta collection and 2) standardized ileal amino acid digestibility (SIAAD) using the ileal digesta collection from high-protein dried distillers' grains (HP-DDG) and corn bran with solubles (CBS). The results of the metabolism trial indicated that AMEn values for HP-DDG and CBS were 3,334 kcal/kg and 2,083 kcal/kg on dry matter (DM) basis, respectively. Concerning the HP-DDG, the digestibility trial resulted in the following SIAAD values and digestible concentrations, respectively: 80.33% and 1.09 for Lys, 85.95% and 1.44 for Met + Cys, 75.58% and 1.24 for Thr, 89.58% and 1.66 for Arg, 84.91% and 1.08 for His, 86.37% and 1.35 for Ile, 90.64% and 4.56 for Leu, 85.76% and 1.80 for Val, and 88.67% and 1.90 for Phe. Concerning the CBS, the following SIAAD values and digestible concentrations were measured, respectively: 79.29% and 0.44 for Lys, 89.57% and 0.31 for Met + Cys, 78.89% and 0.40 for Thr, 92.28% and 0.66 for Arg, 87.48% and 0.36 for His, 93.40% and 0.35 for Ile, 92.27% and 1.01 for Leu, 90.97% and 0.51 for Val, and 88.81% and 0.45 for Phe. The digestibility average of CBS is 88.45% for essential amino acids and 85.21% for nonessential amino acids, whereas the digestibility average of HP-DDG is 85.83% for essential amino acids and 83.83% for nonessential amino acids., (Copyright © 2023. Published by Elsevier Inc.)

Two trials were carried out to assess the effects of different ratios of standardized ileal digestible isoleucine:lysine (SID Ile:Lys) on the growth performance of broiler chickens fed low-protein diets. A total of 1,320 male chickens were distributed in each trial into 6 treatments, with 10 replicates with 22 birds each. A control diet was formulated that satisfied the nutritional requirements of the broilers, and a low-protein diet was formulated with reduced protein content, meeting broiler nutritional requirements, except for the SID Ile levels. Five SID Ile:Lys ratios (56%, 61%, 66%, 71%, and 76%) were obtained by adding l-isoleucine to the low-protein diet. The body weight (BW), body weight gain (BWG), average daily feed intake (ADFI), and feed conversion ratio (FCR) were evaluated from day 1 to day 21 in trial 1, and from day 22 to day 44 in trial 2. ANOVA was performed on the data, and the treatments were compared to the control group using Dunnett's test (P ≤ 0.05). Regression analyses were performed for modeling the variables assessed and the ratios of SID Ile:Lys. There was no significant difference between the treatments on ADFI of birds (P > 0.05). The BW, BWG, and FCR showed a quadratic effect as the SID Ile:Lys ratio increased in low-protein diets in trials 1 and 2 (P ≤ 0.05). In conclusion, the recommended ratio of SID Ile:Lys in low-protein diets for growth performance is around 66% for broiler chickens from 1 to 21 d old and is around 65% for broiler chickens from 22 to 44 d old., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Two trials were carried out to assess the effects of arginine supplementation through ratios of digestible arginine:lysine on growth performance, skin quality and creatine levels in muscle and serum of broiler chickens fed diets reduced in protein content. A total of 1,540 Cobb500 male chickens were distributed into 7 treatments, with 10 replicates with 22 birds each. The experimental diets were based on corn and soybean meal, and a control diet was formulated to satisfy broiler nutritional requirements. A basal diet with reduced protein content was formulated to meet broiler nutritional requirements, except for SID Arg levels. The experimental diets were obtained by adding L-arginine to basal diets, meeting 6 different SID Arg:Lys ratios (94, 100, 106, 112, 118, and 124%). Body weight, body weight gain, average daily feed intake, and feed conversion ratio were evaluated from 01 to 21 d old (trial 1) and from 22 to 44 d old (trial 2). At 21 and 44 d, in trials 1 and 2, respectively, birds were slaughtered to assess skin thickness (ST), skin strength (SS), creatine level in muscle (CRM) and serum (CRS). Data were subjected to ANOVA, and treatments were compared to the control group by Dunnett's test (P ≤ 0.05). Regression analyses were performed to model the variables assessed and the ratios of SID Arg:Lys. The SID Arg:Lys ratios did not affect ADFI of broilers in both trials (P > 0.05), whereas it linearly increased the BW, BWG, and ST, in both trials (P < 0.001). The FCR of broilers linearly decreased, in trial 1 (P = 0.038) and trial 2 (P < 0.001). The CRM of birds had a linear effect (P < 0.001) in trial 1, and a quadratic effect (P = 0.001) in trial 2. The CRS and SS of broilers linearly increased, in trial 2 (P < 0.001). In conclusion, increasing SID Arg:Lys ratios in diets reduced CP enhanced growth performance, skin quality and CR levels in muscle and serum of broiler chickens from 01 to 21 and 22 to 44 d old., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)